This invention relates in general to forming end panels for containers, commonly referred to as cans, and, more particularly, to methods and apparatus for forming can ends from thin sheet material in a single acting press with the can ends having at least one and preferably a plurality of beads formed without unacceptable thinning by flowing material from a shell which is thereby reduced in length resulting in a shortened shell length which is extended during the upstroke of the press to be within required specifications for the can ends.
Ends for closing cans, such as cans for containing foods, are well known in the art. Such can ends are normally made of steel and are formed with concentric beads which permit some flexing of the can ends when secured to can bodies to accommodate pressure changes associated with processing foods within the cans. Conventional can ends include, for example, three beads formed near a crown of the can end with which the can end is secured to the can body. These can ends can be made by blanking a workpiece from a sheet of steel, drawing the workpiece to generate a shallow cup with a crown, and forming the beads between male and female profiled tools which penetrate one another.
Simultaneously drawing the material over each bead profile can result in significant stretching or thinning of the material and coatings on the material, particularly at locations entering a bead. Such thinning of the material around beads of can ends can lead to nonuniform stresses within the material leading to warping or twisting of the can ends, fractures within the bead areas which can lead to "leakers", and cracks in enamel coatings applied to the material to prevent direct contact of the material of the can ends with food contained within cans.
These problems are exacerbated as the canning industry continues to pursue the use of thinner and thinner stock material for making can ends. In this regard, there have been recent efforts to use double reduced steel for making can ends. With such reduced thickness materials, panel fractures also can occur since the material is so thin and is more work hardened. Further, an increased amount of force is required to form the can ends and double reduced steel displays a significant amount of memory leading to spring back which can result in warping and shallow beads in addition to the thinning problems.
There is, thus, a need for improved methods and apparatus for forming beaded can ends from thin sheet materials, such as double reduced steel, which overcome the problems currently being encountered in the art. Preferably, the improved methods and apparatus would employ a single acting press having a fixed base and a movable upper punch assembly.